Strength Of Alkali-activated Slag Research Articles

Chloride Permeability of Alkali-Activated Slag Concretes after Exposure to High Temperatures.

The number of fires in buildings and on bridges has increased worldwide in recent years. As a structural material, the strength of alkali-activated slag (AAS) concrete after exposure to high temperatures has been given much attention. However, research of its durability is still lacking, which limits the application of this type of concrete on a larger scale. In this context, as one of the most important aspects of durability, the chloride permeability of AAS concretes after exposure to high temperatures was examined in this study. The influence of the alkali concentration (Na2O%) and the modulus (Ms) of the activator, as well as the influence of heating regimes, including the heating rate, duration of exposure to the target temperature, and cooling method, was also discussed. The results show that the chloride permeability of the AAS concretes increased with temperature elevation. Due to the interference of pore solution conductivity, the influence of the Na2O% and the Ms of the activator on the chloride permeability of the AAS concretes was not made clear by using the ASTM C 1202 charge passed method; however, after exposure to high temperatures, AAS with a lower Na2O% and lower Ms has lower porosity and may have lower chloride permeability, which needs further investigation. Faster heating for a longer duration at the target temperature and water cooling reduced the resistance of the AAS concretes to chloride permeability as a result of their increased porosity.

Correlating slag chemistry to setting and mechanical behaviors of alkali-activated slag

Aiming at uncovering the critical chemical parameters that govern the performance of alkali-activated slag (AAS), this work investigates the phase assemblage, microstructure, and setting and mechanical properties of AAS prepared using five different slags and two activators (sodium hydroxide or sodium carbonate). The results suggest that the ratio of non-bridging oxygens to tetrahedral cations (NBO/T) of slag structure is an appropriate reactivity indicator, correlating reasonably well with the mechanical performance of AAS at late ages. However, the NBO/T value of slag structure is relatively incompetent in indicating the setting performance of AAS, particularly for the sodium carbonate-activated system. The variability of slag chemistry has considerable impacts on the setting behaviors of AAS, but relatively insignificant effects on compressive strength, suggesting that the strength of AAS is dominated by activator and mixture proportioning parameters. Regardless of activator chemistry, the AAS with a higher amount of hydrotalcite formation tends to have higher compressive strength, implying the beneficial roles of hydrotalcite in microstructure densification and strength achievement.

Bond strength of alkali-activated slag based tunnel fireproof coating material

Abstract The influence of the concentration of sodium hydroxide solution on the tensile bond strength of alkali-activated slags (AAS) used as a tunnel fireproof coating material was studied under t...

Behavior of alkali-activated slag in the presence of different aluminosilicate sources

This article presents an investigation into the performance of alkali-activated slag (AAS) in the presence of different aluminosilicate sources. AAS was individually replaced by 10, 20, and 30 wt. % Metakaolin (MK), Ground ceramic waste (GCW) and ground clay brick waste (GCBW). The results showed that the Na2O/Al2O3 and CaO/SiO2 molar ratio play a crucial role in the behavior of AAS. GCW and GCBW with different contents have positive impact on the compressive strength of AAS, especially at later ages of curing. AAS performed well in the presence of 10 wt. % MK. Meanwhile, 20 and 30 wt. % caused the AAS compressive strength regression. The water demand of AAS increased with an increase in aluminosilicate’s weight percentage. Also, AAS containing GCBW showed the shortest setting times as well as the highest mechanical properties as proved by XRD, FTIR, and SEM.